1. Field of the Invention
The present invention relates to a wet-type electrophotographic image forming apparatus. More particularly, the present invention relates to an oxidation catalyst unit for removing a carrier vapor produced at a fusing unit by oxidizing, and a wet-type electrophotographic image forming apparatus comprising the same and a method thereof.
2. Description of the Related Art
An electrophotographic image forming apparatus scans a laser beam on a photoconductive medium to form an electrostatic latent image, and transfers a visible image formed by attaching a developer onto the electrostatic latent image, thereby printing a desired image.
A wet-type electrophotographic image forming apparatus uses a liquid developer while a dry-type electrophotographic image forming apparatus uses a powder toner. The wet-type electrophotographic image forming apparatus can implement a clearer image, and even a color image of high quality.
The developers consist of a toner and a liquid carrier such as norpar. The norpar is a hydrocarbon-based solvent which is a mixture of C10H22, C11H24, C12H26, and C13H28.
Paper having the developer passes through a fusing unit and causes the toner component in the developer to adhere on the paper, and the liquid carrier such as the norpar is vaporized by a high temperature and discharged in the form of a combustible hydrocarbon gas such as CH4.
The combustible hydrocarbon gas is one of a volatile organic compound (VOC), which contaminates the environment and emits an offensive odor when discharged. Therefore, various methods for removing combustible hydrocarbon gas have been introduced.
Methods for removing combustible hydrocarbon gases known in the art include a filtration method for physically removing gaseous components using a carbon filter such as active carbon, a direct combustion method for combusting gaseous components at an ignition point (approximately 600° C. to 800° C.), and a catalytic oxidation method for combusting gaseous components at a relatively lower temperature (approximately 150° C. to 400° C.) using a catalyst, thereby oxidizing and resolving the components into water and carbon dioxide.
In the filtration method, the carbon filter does not have a capability of resolving the carrier vapors entrained. Therefore, the carbon filter saturated with carrier vapors needs to be replaced with a new one when the carrier vapors are entrained over a predetermined amount in the carbon filter, and such replacement should be frequently made. Furthermore, the direct combustion method is not safe due to the high temperatures generated. Due to the above problems, recently, wet-type electrophotographic image forming apparatus have mainly employed the catalytic oxidation method for removing the carrier vapors.
FIG. 1 is a schematic view of a conventional oxidation catalyst unit. The oxidation catalyst unit 160 comprises a duct 161, a fan 162, a heater 163, and an oxidation catalyst carrying medium 164.
The duct 161 is connected to one side of a fusing unit 150, and guides a carrier vapor V into the oxidation catalyst unit 160 in order to remove the carrier vapor V produced in the fusing unit 150.
The fan 162 is mounted in the duct 161 to forcibly send the carrier vapor V toward the oxidation catalyst carrying medium 164.
The heater 163 raises the temperature of the carrier vapor V up to an activating temperature, for example, 200° C. The oxidation catalyst carrying medium 164 carries a catalyst such as Pt and Pd, which catalyzes an oxidization reaction. The oxidation catalyst carrying medium 164 is mounted behind the heater 163.
The carrier vapor V is partially cooled and condensed in the duct 161 while moving to the oxidation catalyst carrying medium 164. In the conventional oxidation catalyst unit 160, although the condensed carrier vapor V passes through the heater 163, the carrier vapor V does not completely vaporize.
Therefore, the condensed carrier vapor V gets absorbed into a surface of the catalyst in the oxidation catalyst carrying medium 164, in the form of liquid drops 170, thereby diminishing the effectiveness of the catalyst.